Vitamin D metabolism in chronic childhood hypoparathyroidism: evidence for a direct regulatory effect of calcium.
We noted the presence of elevated levels of circulating 1,25-dihydroxyvitamin D (83 pg/ml (200 pmol/L), with low total serum calcium concentration (6.5 mg/dl (1.88 mmol/L), in an untreated adolescent boy with hypoparathyroidism. Furthermore, an inverse relationship between total serum calcium and circulating 1,25-dihydroxyvitamin D levels was evident during treatment with 1,25-dihydroxyvitamin D3. We examined this relationship with a 33-hour intravenous infusion of calcium gluconate in the absence of exogenous 1,25-dihydroxyvitamin D3 therapy. The infusion was accompanied by a gradual increase of both total serum calcium and blood ionized calcium concentrations from hypocalcemic to normocalcemic ranges, and produced a 50% reduction in circulating 1,25-dihydroxyvitamin D values, with minimal changes in circulating phosphorus, magnesium, and 25-hydroxyvitamin D values. These results suggest that calcium-dependent, parathyroid hormone-independent regulation of 1,25-dihydroxyvitamin D production may exist in human beings.
Carpenter
T O
TO
Department of Pediatrics (Endocrinology), Yale University School of Medicine, New Haven, Connecticut 06510.
Insogna
K L
KL
Boulware
S D
SD
Mitnick
M A
MA
D000293:Adolescent; D002117:Calcitriol / Q000378:metabolism*; D002118:Calcium / Q000097:blood / Q000502:physiology*; D002908:Chronic Disease; D006801:Humans; D007011:Hypoparathyroidism / Q000378:metabolism*
D002117:Calcitriol; D002118:Calcium